L.F.
I know its hard to see your little one in pain. Do half and half of 1% hydrocortisone cream and vasoline---make a paste and apply it 6x a day for the next 2 days. If it doesn't get remarkably better, call the doctor again. If you really feel its yeast, you can get over the counter monistat and put it on the outside area of her privates--nothing inside.
IF you are still nursing, breastmilk does wonders for healing many things---I use that whenever my little one has any issues. Hope this helps! good luck.